In the manufacture of microelectronic circuits it is necessary to attach small components to each other both mechanically and electrically in order to provide desired assemblies. For example, a "chip" may be attached to a substrate or mounting board on which other separate components could also be mounted.
The "chip" is typically a small semiconductor device which internally contains a large number of electronic circuits, but which has a relatively small number of terminals for external connections. For example, the chip may have only two input terminals and two output terminals. The chip is usually constructed in such a way that all of the terminals protrude from one flat surface of the device.
The substrate, or mounting board, is generally of a sheet-like configuration having a thickness of a small fraction of an inch. The substrate is generally integrally formed of a ceramic material. Thin strips or pads of a metallic conductor, such as copper, are secured on one face of the substrate.
In the assembly procedure, a number of chips can be mounted on a single substrate. In hybrid circuits, in addition to the chips, other circuit components such as capacitors and inductance coils may be mounted on the same surface of the substrate with appropriate connections to the conductive strips or pads.
One type of assembly procedure is thermocompression in which both heat and pressure are applied at the same time.
Another type of assembly procedure is known as the flip chip assembly. In this procedure the protruding terminals of each chip are placed in engagement with corresponding conductive strips or pads on the substrate. Some type of soldering technique is then used in order to bond the resulting contact pairs together.
Another assembly procedure is known as wire bonding. In that procedure a portion of the substrate surface that may not carry any conductive strips or pads is provided for securing the chip. Conductive strips or pads are provided in adjacent location on the substrate surface. The protruding terminals of the chip are pointed upwards, away from the substrate. The bottom surface of the chip which carries no terminals is then bonded to the surface portion of the substrate that also is devoid of conductive strips or pads. Then, a short length of wire is used to connect each terminal of the chip to a corresponding one of the adjacent strips or pads on the substrate. Separate solder joints are required at each end of each wire.